反季节消涨节律扰动下土壤种子库对消落带植被生态恢复的作用机制

Soil seed banks provide key propagate sources for vegetation regeneration and restoration. The annual fluctuation rhyme on the water-level-fluctuation belt(WLFB) has been changed from "summer flooding-winter drought" to "summer drought-winter flooding" for flood prevention and electricity generation in the Three Gorges reservoir area. Disturbance from the reverse seasonal fluctuation pattern is seriously affecting input and ouput of soil seed bank and changing obviously its composition, distributioan and durability, which further influence vegetation restoration on the WLFB. Quadrats are going to be arranged along flooding gradient on sample plots of natural, seminatural and artificial restoration vegetation distributed on the WLFB in the Three Gorges reservoir region. The composition, horizontal and vertical distribution of soil seed banks and vegetation are going to be researched through field quadrat investigation and germination of seed bank samples, so are the seed spread by water flow and air using seed bank collectors placed in the quadrats. The output of soil seed banks is to be tested by investigating seedling regeration in field and germination of seed bank samples each season during the WLFB appears. The response of composition, distribution, input and output of soil seed banks to the disturbance of reverse seasonal fluctuation rhyme is revealed by analysis the diference among flooding gradients. The sustainability of seed banks and artifitial seed banks, and their response to the disturbance of reverse seasonal fluctuation rhyme are going to be studied by testing the change of seed germination and seed activity of seed banks in a control experiment which simulates different water-level-fluctuation patterns in greenhouse. The effects of soil seed bank on vegetation restoration is concluded according to the relationship between the composition and structure of soil seed bank and vegetation on the WLFB, the dynamic of vegetation restoration and their response to the disturbance of the reverse seasonal fluctuation rhyme. Suggestions will be finally put forward to prompt the ecological restoration and management of vegetation based on the mechanasim of vegetation restoration by soil seed bank on the WLFB.

土壤种子库是植被更新与恢复的基础。三峡工程因防洪与发电的需要,把库区消落带水位消涨节律从原有的 "夏洪-冬旱"变成"夏旱-冬洪"。这种反季节消涨节律的扰动严重影响消落带土壤种子库的输入、输出规律，并使种子库组成、空间分布和可持续性发生明显变化，进而影响到植被的生态恢复。本项目将结合库区消落带自然、半自然和人工植被恢复实践，通过植被与土壤种子库的样方调查、种子库萌发实验、水传播种子输入和空气传播种子输入现场实验、土壤种子库幼苗更新野外调查、消涨节律对土壤种子库和人工种子库输出与持续性影响的模拟控制实验等方法，研究不同恢复措施下消落带土壤种子库的组成与结构、空间分布、输入与输出以及持续性的特征及其对不同消涨节律的响应，并结合土壤种子库与植被的相关性和消落带植被的恢复动态，揭示反季节消涨节律扰动下土壤种子库对消落带植被恢复的作用机制，为利用土壤种子库进行水库消落带植被恢复与管理提供科学依据。

为了探究三峡库区反季节水位消涨对种子库的作用机制，本研究围绕所拟定的研究目标与内容，在香溪河、衫木溪、万州和忠县等地的消落带设置了长期样地，对不同恢复模式下的消落带开展了植被与土壤种子库的样方调查和水传播种子输入和空气传播种子输入现场实验，并利用所采集样品进行了种子库萌发实验、消涨节律对土壤种子库和人工种子库输出与持续性影响的模拟控制实验。结果显示，反季节水位消涨对土壤种子库的组成和空间分布都有显著影响。水位涨落会影响种子空气传播到土壤的进程，但能促进种子的二次传播，调整种子库的空间分布。受反季节水位消涨的影响，消落带土壤种子库的物种多样性和密度显著低于消落带上缘，消落带中部的土壤种子库的密度和物种多样性高于消落带的中上部和下部。土壤种子库的可持续性随着水淹周期的延长而不断下降。人工植被恢复能有效增加土壤种子库的密度，但是对土壤种子库多样性的作用有限。研究还发现土壤种子库与地上植物群落有着较为紧密的相关性，反季节水淹对土壤种子库的影响会进一步影响到植物群落的演变。